Polycarbonates have previously been produced from glycols by reacting with phosgene or bis-chloroformates followed by removal of hydrochloric acid from the reaction vessel. Polycarbonates prepared by the condensation of glycols and dialkyl carbonates have been described by Carothers and others. Alkaline catalysts were used and the alcohol by product removed by heating.
Glycols have also been esterified with diaryl carbonates in the absence of catalyst whereby phenols or substituted phenols are distilled off. Polycarbonates have also been manufactured by polycondensation of bisalkyl or bisaryl carbonates of dihydroxy compounds.
Polycarbonates produced by these methods may have a functionality less than two due to inadequate or incomplete esterifiction or transesterification which often prevents the products from forming high molecular weight polymers by subsequent reactions.
Polycarbonates have also been prepared by polymerization of ethylene carbonates under pressure using basic catalysts and a minor amount of glycol as initiator. These products are low in carbonate and high in ether groups concentration due to decomposition of the ethylene carbonate.
It has been reported that polycarbonates can be prepared by the ester interchange reaction of a glycol and an alkylene carbonate, for example, ethylene carbonate, only in the presence of alkaline or acid catalysts. These catalysts remain in the polycarbonate and can have an adverse effect on quality.
It is an object of this invention to provide an efficient process for preparing polycarbonates.
Another object of this invention is to provide methods of making high molecular weight polycarbonates with desired functionality and having good quality without inherently incorporated unwanted catalyst traces.
Still another object of this invention is to provide methods in accordance with the preceding objects which can be carried out in commercial production facilities at reasonable rates with good repeatability.